基于能谱积分方法的中子诱发235U裂变产物产额-能量关系检验研究

Validation for Energy Dependence of Fission Product Yields of Neutron-induced 235U Fission Based on Energy Spectrum Integral Method

  • 摘要: 裂变产额随入射中子能量的变化关系(产额-能量关系)是核能发展和核技术应用的关键基础数据,是裂变产额研究的重点。针对不同评价方法给出的产额-能量关系存在差异的问题,本文提出一种间接检验方法。以252Cf自发裂变中子谱、中子诱发235U裂变截面及裂变产物核95Zr、99Mo和147Nd的产额-能量关系为例,通过数值积分方法计算裂变谱中子等效产额,并与实验测量值对比。结果表明,该方法可为裂变谱能区产额-能量关系的合理性提供间接检验。在热能点至4 MeV之间,产额-能量关系的变化趋势对裂变谱中子等效产额计算影响较大,这与裂变谱中子在该能区份额较大有关。本工作为实验上开展产额能谱积分实验测量从而检验特定能区产额-能量关系的合理性提供了思路。

     

    Abstract: Fission product yields (FPY) have long been recognized as one of the most distinctive characteristics of the fission process, showing a strong correlation with excitation energy and the fissioning species. The energy dependence of FPY is essential data for the advancement of nuclear energy and the enhancement of nuclear technology applications. As such, it has become a focal point in both experimental and theoretical research on FPY. Given the intrinsic complexity of the fission mechanism, conducting consistent and systematic studies on the dependence of FPY on incident neutron energy remains a challenging task. To address this, advanced nuclear models of the fission process are being developed, alongside experimental measurements of both integral and differential energy-dependent FPY. A significant gap in current research lies in the validation of energy-dependent FPY data for the three major actinides of 235U, 238U, and 239Pu across a wide energy range. This lack of comprehensive study provides the primary motivation for this work. A novel approach was introduced to validate the energy dependence of FPY based on a well-defined neutron-energy spectrum and the cross section of fission nuclei. The effectiveness of this method was demonstrated by validating energy-dependent FPY data using the neutron spectrum from 252Cf spontaneous fission and the neutron-induced 235U fission cross section as a case study. The primary focus is on three key fission products, 95Zr, 99Mo, and 147Nd, which are critical nuclides in the fission process. The equivalent yields within the fission spectrum’s neutron energy range were then calculated, and these calculations were compared to the integral yields measured in the 252Cf spontaneous fission neutron spectrum. The results indicate that comparing the fission spectrum neutron equivalent yields with integral measurement yields is a reliable method for assessing the validity of yield-energy dependent FPY data, particularly in the fission spectrum neutron energy range. The trend in the yield-energy dependence between the thermal energy point and 4 MeV has a significant impact on the calculated equivalent yields of fission spectrum neutrons, due to the fact that fission spectrum neutrons exhibit the highest neutron flux in this energy range. These findings emphasize the importance of understanding the yield-energy dependence within a certain energy range and illustrate the method’s potential for improving the reliability of FPY models. An idea to indirectly verify the validity of the yield-energy dependence by carrying out integral fission product yield experiments was proposed, offering valuable insights for future research in this area.

     

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